MR. J. L. CLARKE OK THE INTIMATE STRUCTURE OF THE BRAIN. 
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parts of them are separated from the rest of the antero-lateral columns by a deep notch 
on each side. Fig. 18, Plate IX. represents the posterior part of the right lateral half of 
the medulla somewhat higher up. Here the posterior pyramid ( b ) has increased in dimen- 
sions and become completely filled with grey substance. The restiform body ( c ) has also 
enlarged and is singularly prominent. The grey substance differs in some respects from 
that of the human medulla. The part o of fig. IT has now enlarged into a broad mass, 
from which a multitude of conspicuous fibres radiate like a brush to a remarkable group 
of cells situated near the surface of the column (c). These cells are much larger and more 
diversified in shape than those of the inner part (o) of the restiform nucleus, and are 
united together by their processes in a network. This grey mass exists likewise in Man, 
but is not so largely developed. It is seen to commence in fig. 5, Plate VIII. at c' e' v 
as a small offset from o, and to increase in size through the rest of the figures. In 
Man there are many more fibres constituting the network than in the Ape, and the 
cells are somewhat smaller and more elongated. Fig. 26, Plate X. represents some of 
the cells from the Ape, magnified 220 diameters. They are in close vicinity of bundles 
of longitudinal fibres. In fig. 19 this outer nucleus of the restiform body has increased 
in dimensions, and is united immediately, instead of by radiating fibres, to the inner 
restiform nucleus (o), which, like the posterior pyramid (b), is also larger than in the 
preceding figure. This inner nucleus ( o ) is now seen to consist of numerous oval, glo- 
bular, crescentic, or irregular masses of granular substance, with small, and, for the 
most part, round, oval, or pyriform cells, which contrast strongly with the large, vari- 
ously-shaped, and branched cells of the outer nucleus (c'). At each side of the canal, 
1 1' has now taken the form of an oval mass, the lower part of which has become the 
nucleus of the hypoglossal nerve; while the upper or posterior part ( t ), which is joined 
to its fellow by a light commissure, has become the nucleus of the spinal-accessory nerve. 
At this upper or posterior part it is directly continuous with the posterior pyramid ( bb ") ; 
but its outer side is separated from o, the inner restiform nucleus, by two sets of fibres, 
the one proceeding from that nucleus and from the posterior pyramid, to the remains of 
the anterior cornu, and the lower end (W) of the olivary body of the same side ; while 
the other set (n) proceed from the lateral column at the side of the spinal-accessory 
nucleus (t) to the olivary body, and back of the anterior pyramid of the opposite side 
(yy), decussating with their fellows from the other half of the medulla. As usual, the 
caput cornu (e), or dilated extremity of the posterior horn, has been pushed forward from 
its cervix by the development of the post-pyramidal and restiform- ganglia (b and o ). The 
anterior pyramids (y, y) are much larger than in any of the mammalia (compare figs. 13, 
14, Plate XII., and figs. 15, 16, Plate XIII. of my Memoir on the Medulla Oblongata, 
Phil. Trans. 1858). Fig. 20, Plate IX. represents a transverse section of the right 
lateral half of the medulla of the Monkey, at the point of the calamus scriptorius, where 
the connexions between the spinal-accessory nuclei and the posterior pyramids of oppo- 
site sides are broken through. The two oval masses ( t , t') are separated behind by the 
opening of the canal into the fourth ventricle, and resemble a pair of acorns joined at 
